For promoting the growth of animals such as livestock, antibiotics such as tetracycline and avoparcin have heretofore been used by being added to feed as fattening promoters. However, these antibiotics often induce resistant bacteria through mutation in the body of animals. In addition, they may remain in the body of animals, and the human beings who have eaten the meat of the animals shall inevitably take the antibiotics. As a result, the potency of antibiotics serving as medicines will be thereby lowered.
Recently, therefore, substances except antibiotics have been investigated for fattening promoters for animals. For example, fumaric acid is used as a fattening promoter.
On the other hand, gluconic acid which is one typical example of hexose-derived acids has heretofore been widely used. For example, its intramolecular ester compound, glucono delta lactone is known as a coagulant for tofu (soybean curd); and calcium gluconate is known as a calcium supplement. In addition, sodium gluconate and potassium gluconate have been officially approved as food additives recently and are used in various edibles (International Patent No. WO94/09650).